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Echolocation British engineers have taken inspiration from dolphins for a new type of radar device that could easily track miners trapped underground or skiers buried in an avalanche.

The device sends out two pulses in quick succession to locate a semiconductor device, while at the same time cancelling any background "noise" from other objects.

With more accuracy and speed than conventional radar, the device was able to pick up roadside bombs, bugging devices or mobile phones even in areas with a lot of metal "clutter", says study co-author Timothy Leighton of the University of Southampton's engineering faculty.

The team also built a small, cheap tracker that can be placed in the helmet of a miner or search and rescue worker or even a skier's boots and found with their device, says Leighton.

He says the research was triggered by curiosity of how dolphins can "see" beyond the vast clouds of bubbles they blow to herd their prey into smaller groups for feeding.

"I was thinking to myself that dolphins should not be able to see fish with their sonar in these bubble clouds unless they are doing something very clever that manmade sonar cannot," says Leighton.

"I sat and thought: 'If I was a dolphin what kind of pulse would I send out in order to see these fish in bubble clouds?' and then I decided on a pulse that was a positive and negative pulse."

And so he built a radar system that sends out pulses in pairs, with the second having the reverse polarity of the first. Ordinary radar sends out a single radio pulse.

When the new, twin pulses hit wood or foliage, rocks or most metals, you get back the same two pulses you had sent out: a positive and a negative -- effectively cancelling each other out, says Leighton.

"But if it hits a semiconductor device, then it takes that pulse of a negative polarity and turns it into a positive polarity. It makes everything positive. They come back very strongly because you're adding a positive to a positive so you get a very strong signal."

Tracking rescue workers

The team then took it further, building a semiconductor tracker that weighed less than 2.0 grams, cost less than a euro and was easily picked up by the new device.

"If you have rescue workers going into a building that might collapse or mineworkers going underground, you can give them these and it will tell you exactly where they are and who they are because you can tune them to identify the person," says Leighton.

But even if a person did not have the tag when they were in a building that collapsed, the device could be used to trace mobile phones even if they were switched off or their batteries were dead.

As for the dolphin: while acting as an inspiration for the technology, Leighton and his team later discovered this was not how the animals' sonar worked.

Dolphins also send out twin pulses, but theirs vary in amplitude, not polarity, he says.